1. Field of the Invention
The present invention relates to a turbocharger.
2. Description of the Related Art
Turbochargers have been known as being used to increase output of engines by being connected to the engines and the like. As boost pressure of a turbocharger becomes higher, the subsequent flow rate and pressure of the exhaust gas become higher. As the torque of the turbocharger becomes higher, the boost pressure becomes much higher. As a result, the engine and the turbocharger become more likely to suffer damage. To avoid this, some turbochargers have a function of suppressing the pressure of the exhaust gas flowing into a turbine housing by making part of the exhaust gas flow from the engine to the downstream of the turbine while bypassing the turbine.
The turbine housing of the turbocharger having the foregoing function is provided with a through-hole making the upstream and downstream of a turbine impeller communicate with each other. In other words, the through-hole forms a bypass passage. Outside the turbine housing, a wastegate valve is placed to face the through-hole. The wastegate valve closes and opens the bypass passage by coming into contact with and getting away from the through-hole.
The wastegate valve is attached to a support plate which is moved by an actuator, and works together with the support plate. If, however, the wastegate valve and the support plate are completely fixed to each other, the wastegate valve cannot close the through-hole when force tilting the wastegate valve acts on the surface provided with the through-hole, and a gap occurs between the wastegate valve and the through-hole. To avoid this, a turbocharger disclosed in Japanese Patent Application Publication JP11-044219A (PTL 1) is provided with a clearance between the wastegate valve and the support plate. To put it specifically, the wastegate valve includes a valve body, and a projecting portion which projects from the valve body. On the other hand, the support plate is provided with an insertion hole. The projecting portion is inserted into the insertion hole, and a part of the projecting portion sticking out of the insertion hole is swaged with a washer or the like while retaining the clearance between the valve body and the support plate.
However, there is a backlash between the washer and the support plate, vibration of the engine makes the wastegate valve and the support plate repeatedly come into contact with and get away from each other, thereby causing noises (chattering). To avoid this, a turbocharger disclosed in WO2010/135104A2 (PTL 2) is provided with a belleville spring between the valve body and the support plate, and suppresses noises by keeping the valve body and the support plate in contact with the biasing force of the belleville spring.